How to Eliminate Noise and Vibration in Stepper Motors

Where Does the Noise of Stepper Motors Come From?

Stepper motors are known for their simplicity, convenient control, safety, low cost, high torque at stop, and the ability to provide substantial torque at low speeds without requiring a gearbox. In comparison to brushless DC and servo motors, stepper motors can achieve position control without complex control algorithms or encoders. They find applications in precise positioning requirements across various fields, including industrial automation, 3D printing, medical equipment, optics, and more.

However, one drawback of stepper motors is their relatively high noise levels, especially at low speeds. The vibrations primarily stem from two aspects: the step resolution of the stepper motor and issues related to chopping and Pulse Width Modulation (PWM) modes.

Step Angle Resolution and Microstepping

Standard stepper motors have 50 poles, resulting in 200 full steps, or 1.8° per step in a full-step mode. Some stepper motors have smaller step angles, such as those requiring 800 steps for a full rotation. Microstepping subdivides these steps further. Initially, these motors were used in full-step or half-step modes, providing rectangular current waveforms to coils A (blue) and B (red), depicting a complete 360° cycle. In these modes, either maximum current (full power) or no current flows through the coils at the 90° phase shift point, as seen in Figures 1 and 2.

Each complete electrical cycle consists of 4 full steps or 8 half steps. For a stepper motor with 50 poles, 50 electrical steps are needed for one full mechanical rotation (360°).

Figure 1: Full-step operation

Figure 2: Half-step operation

Low Step Resolution Modes

Low step resolution modes, such as half-stepping or full-stepping, are the main sources of stepper motor noise, causing significant vibrations in the mechanical system, especially at low speeds and near mechanical resonance frequencies. At higher speeds, the effect is reduced due to inertia, and the motor’s rotor can be considered as a harmonic oscillator or a pendulum, as illustrated in Figure 3.

Figure 3: Pendulum behavior of the rotor leads to vibrations

After new current vectors are output from the driver, the rotor moves to the next full or half-step position according to the new position command. Similar to a pulse response, the rotor produces overshooting and oscillations around the new position point, resulting in mechanical vibrations and noise. To reduce these vibrations, microstepping was introduced, subdividing a full step into smaller parts. Typical subdivision factors are 2 (half-stepping), 4 (quarter-stepping), 8, 32, and even larger subdivisions.

The current in the stator coils is not at its maximum (full current) or zero, but at an intermediate level, closer to a sine wave compared to the square wave of 4 full steps. The rotor of the permanent magnet is positioned between two full step positions (synthetic magnetic field positions). The maximum subdivision factor depends on the driver’s A/D and D/A capabilities. TRINAMIC’s drivers and controllers can achieve up to 256 subdivisions (8-bit) with an integrated sine wave table, enabling precise angle control.

Chopping and PWM Modes

Another source of noise and vibrations is traditional chopping and Pulse Width Modulation (PWM) modes. While coarse step resolutions are the main factor in generating vibrations and noise, the issues caused by chopping and PWM modes are often overlooked.

Traditional constant PWM chopping operates with a fixed relationship between fast decay and slow decay, causing the current to reach the desired target current only at its maximum value. As a result, the average current is lower than the target current, leading to vibrations.

In TRINAMIC’s SpreadCycle PWM chopping mode, a hysteresis-based decay function is automatically applied between slow and fast decay phases. The average current reflects the desired current, and there is no transitional period at the sine wave zero crossing, reducing current and torque fluctuations. The motor operates more smoothly and stably under SpreadCycle PWM chopping mode compared to traditional constant PWM chopping modes.

Achieving Complete Silence with Stepper Motors

While high microstepping resolves many low-frequency vibrations, advanced current control PWM chopping modes, such as TRINAMIC’s SpreadCycle algorithm, significantly reduce vibrations and tremors in the hardware. However, noise and vibrations caused by current control chopping modes, such as variations in coil synchronization, voltage adjustments of a few millivolts on detection resistors, and PWM timing errors, still exist. These issues are unacceptable in applications that demand silence, slow or medium-speed motion, and noise-sensitive environments.

TRINAMIC’s StealthChop algorithm is a hardware-based solution that achieves true silence with stepper motors. It employs a new technique based on voltage modulation rather than current modulation, ensuring silent and smooth motion.

The TMC5130 is a compact stepper motor driver with the StealthChop mode. TRINAMIC has integrated voltage control with current control, minimizing current fluctuations by using current feedback to modulate voltage. This adaptive voltage modulation eliminates the minor oscillations introduced by direct current control algorithms.

StealthChop can drive stepper motors nearly silently, with noise levels below 10 dB, significantly quieter than traditional current control methods.

How Does StealthChop Affect Stepper Motors?

Stepper motors remain economical and have continued to use the same materials, production processes, and assembly techniques over the years. However, modern stepper motors are driven by simpler control units, advanced algorithms, and highly integrated microelectronics, unlocking their full potential.

Stepper motors are now being driven by more advanced algorithms and highly integrated microelectronics, which enable better control, data acquisition, and real-time processing. StealthChop is a prime example, tightly integrated with PWM chopping, and it revolutionizes the way stepper motors operate, making them virtually silent and efficient.

TRINAMIC offers modules with StealthChop capabilities, including single-axis, three-axis, and six-axis control modules. In contrast to traditional control methods (pulse/direction), TRINAMIC’s intelligent stepper motor control solutions support bidirectional communication, enabling monitoring of different states and diagnostic information. This enhances system reliability and performance.

StealthChop technology is particularly suitable for applications requiring low noise levels, such as 3D printing, CNC machining, medical diagnostics, and more.